1. Field of the Invention
This invention relates to a novel method for nucleating engineering thermoplastic resins utilizing a polyolefin resin as a nucleating agent. In several preferred embodiments of the invention, polyethylene is used as a nucleating agents for blends of poly(phenylene ether) resins with polystyrene resins, for polycarbonate resins, and for blends of polycarbonate resins with rubber modified vinyl aromatic graft copolymers.
2. Brief Description of the Related Art
The production of thermoplastic structural foam articles by injection molding processes using either an inert gas such as nitrogen, a chemical blowing agent, or mixtures thereof, are well known in the art. Such processes typically use a thermoplastic resin which contains an amount of a nucleating agent which is added for the purpose of assisting in the formation of cell structures during the foaming process. The use of some nucleating agents such as clay have, however, in some circumstances can show an inability to uniformly expand the thermoplastic resins resulting in non-uniform cell structures and higher density foams than are desired.
Fluoropolymers, such as poly(tetrafluoroethylene) resins, have been described as nucleating agents for various engineering resins. The fluoropolymers are expensive and often create difficulties in handling such as poor powder flow during compounding of chemical blowing agent concentrate, the population of cell is predetermined by the poly(tetrafluoroethylene) population.
Accordingly, there continues to be a need for a nucleating agent which will enhance the uniformity of the cell structures formed upon expansion of the resin.